J3B1  NSS/MIC/RTSD Joint Session

Wednesday, Nov. 4  10:30-12:30  Golden Pacific Ballroom

Session Chair:  Paul Lecoq, CERN, Switzerland; Benjamin Tsui, Johns Hopkins University, United States

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(10:30) J3B1-1, Diamond Detectors as Microdosimeters for Ion-Beam Therapy

P. Solevi1, G. Magrin1, C. Verona2, G. Verona-Rinati2, M. Jakšic3, D. Moro4, R. Mayer1

1EBG MedAustron, Wiener Neustadt, Austria
2Department of Industrial Engineering, University of Rome Tor Vergata, Rome, Italy
3Ruder Boškovic Institute, Zagreb, Croatia
4Laboratori Nazionali di Legnaro (INFN), Legnaro, Italy
Chemical vapor deposition (CVD) diamond detectors have been suggested as ion-beam therapy microdosimeters since they can be manufactured with small cross sections and thin shapes, ideal to cope with the high fluence rate. However the sensitive volume of solid state detectors significantly deviates from conventional microdosimeters, with diameter that can be up to 1000 times the height. This difference requires a redefinition of the concept of sensitive thickness and a deep study of the secondary to primary radiation, of the wall effects and of the impact of the orientation of the detector with respect to the radiation field. We studied through Monte Carlo simulations the potential of diamond detectors to determine the radiation quality of ion-beams. Highly pixellated geometries provide the possibility to study the structure of the primary ion track penumbra, and to identify through different criteria multiple fragment tracks. The experimental characterization of diamond detectors irradiated by mono-energetic ion microbeams at the facility of Ruder Boskovic Institute in Zagreb is also described. The spatial response and the hardness of the detector are studied at different ion-beam rates and integrated dose. Concerning the radiation hardness, in terms of clinical use, a 3% detection efficiency loss has been measured over the full dose delivered to 1000 patients. The characterization and verification of the working parameters of such a compact solid state detector is the fundamental step towards its clinical use, not limited to the definition of the radiation quality.

(10:45) J3B1-2, Evaluation of a Two-Channel Coplanar CZT Detector Prototype for Atmospheric Radioxenon Measurement

L. Ranjbar, A. T. Farsoni, E. M. Becker, S. A. Czyz

Nuclear Engineering & Radiation Health Physics, Oregon State University, Corvallis, United States
Detection and identification of radioxenon isotopes is critical to the efforts of the Comprehensive Nuclear Test Ban Treaty Organization (CTBTO) to detect nuclear detonations, and radioxenon detectors can be found on many International Monitoring System stations. Most current radioxenon detectors are based on beta-gamma coincidence techniques using scintillator detectors. A new radioxenon detection system is being developed at Oregon State University in an effort to improve upon these detectors by using coplanar CdZnTe (CZT). Removing the need for a plastic scintillator for distinguishing beta particles and conversion electrons from gamma rays and X-rays eliminates the memory effect. Coplanar CZT also has better energy resolution than scintillator materials. These two properties are expected to significantly improve the Minimum Detectable Concentration for the four radioxenon isotopes of interest: 131mXe, 133Xe, 133mXe, and 135 Xe. The prototype detection system being developed uses two 19.4 x 19.4 x 5 mm3 coplanar CZT detectors on opposite sides of an aluminum gas cell to detect coincident radiation events from the radioxenon isotopes of interest. The optimal coplanar pattern for these crystals was determined by quantitatively comparing simulated weighting potentials among many different coplanar designs. The optimal design was then deposited onto the two CZT crystals via thermal evaporation using a shadow mask. Pulses from these detectors are conditioned in an analog subtraction circuit, digitized, and analyzed offline for greater flexibility in determining optimal operation parameters for this prototype design. Characterization will be performed with sealed laboratory tube sources as well as radioxenon isotopes generated via irradiation of enriched stable xenon isotopes in the OSU TRIGA reactor.?

(11:00) J3B1-3, Multilayer Compton Camera Based on Timepix Technology with Si and CdTe Sensors

J. Jakubek1,2, M. Jakubek1, P. Soukup1, D. Turecek1, J. Uher1, S. Vahanen3

1WIDEPIX ltd., Prague, Czech Republic
2Institute of Experimental and Applied Physics of the Czech Technical University in Prague, Prague, Czech Republic
3ADVACAM ltd., Espoo, Finland
In this contribution we present a very compact detector system for imaging with gamma-rays using Compton camera principle. The system consist of at least two layers of hybrid pixel detectors Timepix with sensors optimized for gamma-ray tracking. The front detector layers (scattering) are made of silicon of various thickness (up to 1 mm) while the last layers (absorbing) are equipped with thick CdTe or CZT sensors up to 2 mm in thickness. The total absorption of the whole detector can be very high if several CdTe or CZT layers are used. The maximal number of layers is not limited but the practical evaluation was performed for 2 and 4 layers. The palm-top size of the system allows to surround inspected space with several units performing fully tomographic measurement. High granularity of Timepix detector allows in high energy cases determination of the direction of the recoiled electron. In these cases the proper energy measurement is difficult since the recoiled electron often leaves the sensor not depositing its full energy. The knowledge of scattering plane is sufficient for back-projection and 3D reconstruction of the radiation field. This method is combined with standard method of Compton camera based on energy measurement. Further improvement of the imaging quality is reached exploiting knowledge of a global energy spectrum for inspected radiation field. Such global spectrum is either known in advance (e.g. in case of medical SPECT) or it is measured by the same device during the experiment (resolution of 60 keV at 1.33 MeV). The angular resolution of the presented Compton camera depends on detected energy and reaches units of degrees. Several first results obtained with Timepix3 detector will be presented as well. The Timepix3 technology is very advantageous since it allows to measure both: the time stamp and the energy in parallel for each pixel with much higher precision than older Timepix.

(11:15) J3B1-4, Helium Radiography with a Compact Semiconductor Detector - First Results

T. Gehrke1,2, R. Gallas2, G. Arico1,2, J. Jakubek3, O. Jaekel2,1, M. Martisikova1,2

1University Hospital, Heidelberg, Germany
2German Cancer Research Center (DKFZ), Heidelberg, Germany
3Institute of Experimental and Applied Physics, Prague, Czech Republic
In ion beam radiotherapy, a very precise target positioning is required and therefore a monitoring of the target position is desirable. For this purpose, ion beam radiography (IBR) could complement the conventional imaging modalities. In principle, IBR provides a high soft-tissue contrast and causes less dose to the patient compared to x-ray projections. However, suitable detectors are still lacking. This contribution introduces a method of IBR using a compact and pixelized semiconductor detector. The Timepix detector has a sensitive area of 2 cm2 consisting of silicon. Its high spatial resolution (pixel pitch: 55 µm) enables single ion detection with energy sensitivity in each pixel. Concerning IBR, helium ions represent a promising trade-off between protons and carbon ions because of less multiple Coulomb scattering than for protons and lower dose to the patient than for carbon ions. Measurements with helium beams, accelerated up to 220 MeV/u, were performed at the Heidelberg Ion-Beam Therapy Center (HIT). In the experimental set-up, helium ions passed through a 160 mm thick PMMA phantom, which has a step of 1 mm to be imaged. A stack of three Timepix detectors was placed behind the phantom and facilitated to measure the energy loss and direction of single impinging ions and to distinguish between different ion species. Using all these information, helium radiographies were reconstructed. The obtained images demonstrate, that a relative thickness difference of 0.6 % is resolvable. The contrast-to-noise ratio and spatial resolution of the radiography was shown to improve by distinguishing between different ions species and taking into account the direction of every single impinging ion. In conclusion, we have shown that helium radiography with the Timepix detector provides a high thickness resolution of the imaged object. Additionally, the distinction of different ion species and the direction information further improves the quality of image.

(11:30) J3B1-5, iMPACT: innovative pCT scanner

P. Giubilato1, W. Snoeys2, S. Mattiazzo1, N. Pozzobon1, D. Pantano1, D. Bisello1, T. Kugathasan2, J. Rousset2, H. Mugnier2, C. A. Marin Tobon2

1Physics, Padova University and INFN, Padova, Italy
2PH-ESE-ME, CERN, Meyrin, Switzerland
We illustrate the iMPACT (innovative Medical Protons Achromatic Calorimeter & Tracker ) project, which will develop a proton Computed Tomography (pCT) scanner capable of acquiring a target full 3D image with a 10s exposure, therefore opening the way to the practical application of proton imaging technique in medical radiotherapy treatments. Such cutting-edge particles scanner combines innovative ideas devised for the future High Energy Physics experiments together with original developments in the microelectronic field to enable charged particles tracking at the GHz scale. In recent years the use of hadrons (1H and 12C ions) for cancer radiation treatment has become an established technique and many facilities are currently operational or under construction worldwide. To fully exploit the therapeutic advantages offered by hadron therapy, precise target (body) imaging for accurate beam delivery is decisive. pCT systems, currently in their R&D phase, provide the ultimate in low dose (< 2 mGy), 3D imaging for hadrons treatment guidance. Key components of a pCT system are the detectors used to track the protons and measure their residual energy. The iMPACT project envisions a proprietary monolithic pixels tracking detector and an innovative achromatic calorimeter to improve current pCT imaging speed by more than a factor 100, leading to potential recording times of few seconds for a full 3D target image (compared to present minutes). The iMPACT detector will also have higher spatial resolution (equal or better than 10 µm) and lower material budget (by a factor 10) respect to state of the art systems, further enhancing 3D imaging accuracy. Not least when considering actual industrial application, production costs will be far lower than existent systems, because all sensors will be designed with commercially available technologies, making it possible to move pCT from the academic research realm to that of viable medical equipment.

(11:45) J3B1-6, New Silicon Microdosimetry Probes for RBE and Biological Dose Studies Using Stationary and Movable Targets in 12C Ion Therapy

L. J. Chartier1, L. T. Tran1, D. Bolst1, A. Pogossov1, S. Guatelli1, M. Petasecca1, D. Prokopovich2, M. Reinhard2, V. L. Perevertaylo3, G. Pellegrini4, C. Fleta4, M. Jackson5, N. Matsufuji6, A. B. Rosenfeld1

1Centre for Medical Radiation Physics, University of Wollongong, Wollongong, Australia
2Institute of Materials Engineering, Australian Nuclear Science and Technology Organisation, Lucas Heights, Australia
3SPA-BIT, Kiev, Ukraine
4Institute of Microelectronics of Barcelona, Centre Nacional de Microelectronica, Barcelona, Spain
5University of New South Whales, Sydney, Australia
6Research Centre for Charged Particle Therapy, National Institute of Radiological Sciences, Inage, Japan
New silicon microdosimetry probes for RBE and biological dose studies of stationary and moving tagets have been developed by the Centre for Medical Radiation Physics, University of Wollongong, Australia. The new probe utilises the CMRP Bridge Microdosimeter and is capable of measuring microdosimetric spectra with lineal energies as low as ~ 0.6 keV/�m. An XY-stage was built using a MakerBot Replicator 3D-printer to move the probe in a PMMA water tank, controlled remotely using Arduino-driven stepper motors. The response of the microdosimeter probe to a 290 MeV/u 12C 6cm SOBP beam in a water phantom at the Heavy Ion Medical Accelerator in Chiba (HIMAC), Japan are presented. The results showed that the effect of motion can lead to a shift of the microdosimetric spectrum and consequently the RBE. This study demonstrated a new, simple and fast method of quality assurance for movable target treatment in charged particle therapy using a high spatial resolution microdosimeter probe with low-noise electronics.

(12:00) J3B1-7, Development of GammaScout Bi-Modality Endocavity Probe for Prostate Cancer Imaging

Y. Cui1, T. Lall2, F. Daloz3, A. Fenster4, G. S. Camarda1, A. Hossain1, U. N. Roy1, G. Yang1, A. DharniDharka3, J. Ionson2, R. B. James1

1Brookhaven National Laboratory, Upton, NY, USA
2Hybridyne Imagine Technologies, Inc., North York, ON, Canada
3GE Healthcare, Phoenix, AZ, USA
4Center for Imaging Technology Commercialization, London, ON, Canada
Abstract – Advanced development of Cadmium Zinc Telluride (CdZnTe) detectors has motivated its application in medical imaging. Over the past few years, we successfully developed a compact trans-rectal gamma camera (ProxiScan™) using CdZnTe detectors to image prostate cancer. Recently, we improved the technology by developing a bi-modality imaging probe, GammaScout, which combines the ProxiScan™ gamma camera with ultrasound imaging. Several engineering prototypes of the new device have been built. New graphical user interface (GUI) software for image acquisition and algorithm for co-registration of the gamma and ultrasound images are being developed. In this presentation, we will introduce the design of the new imaging probe and discuss the test results with prostate phantoms.

(12:15) J3B1-8, invited, Dose Minimization for Affordable CZT Detector Arrays Designed for Molecular Imaging

J. W. Hugg, S. Soldner, B. Harris

eV Products division, Kromek USA, Saxonburg, PA, USA
AIMS Both the Bridgman and THM growth processes can produce CZT detectors capable of molecular imaging applications, but the THM process is more uniform and has higher yields, thus the potential for lower costs. CZT detector arrays have been used in several molecular imaging applications, including small-animal SPECT, cardiac SPECT, and molecular breast imaging (MBI). Both dose and exam time should be minimized without compromising the diagnostic content. METHODS In a molecular imaging system, the interplay of gamma detector, collimator, and image reconstruction software determines image quality and dose-time-FOV tradeoffs. Integration of pixelated CZT detectors with advanced ASICs and readout electronics improves system performance. Analyzing the cathode and neighboring pixel signals provides 3D sub-pixel interaction position, correcting spectral distortion with a corresponding boost in photopeak efficiency, thus improving dose and exam time. With 3D position comes more flexibility in collimator design and optimization for system efficiency. Iterative statistical image reconstruction makes more efficient use of the information in molecular images. RESULTS Because of the initial high cost of CZT, the first clinical applications have been limited to small FOV, such as heart and breast. Radiation doses were initially high and exam times long. Advances in detectors, collimators, and image reconstruction have significantly improved efficiency of CZT-based molecular imaging systems and the cost of CZT detectors has steadily declined. For example, a dual-camera CZT detector MBI system with registered square parallel-hole collimator can operate effectively at a whole-body dose of Tc-99m equivalent to the screening mammography dose. CONCLUSION Continual improvements in CZT detector arrays for molecular imaging, coupled with optimal collimator and image reconstruction, result in minimized dose and exam time. With CZT cost improving, more clinical applications are expected.